A standard pyrotechnic release unit such as described in U.S. patent publication 2004/0255811 has a hermetically sealed pyrotechnic pressure insert that is installed at a rear end of a casing and that is comprised of a support plug carrying a gas-forming pyrotechnic charge. A detachable pin is inserted into an opposite front end of the casing at a spacing from the charge. A first securing point is provided on the casing and a second securing point is arranged on the pin that itself is anchored on the casing by an arresting and force-limiting element. The support plug is rearwardly braced so that it is not blown out of the rear of the casing when the charge explodes. This bracing can be done by crimping over the rear end of the housing after installing the support plug and charge, or by forming the housing with a mainly closed rear wall and installing the support plug and charge through the front end before the detachable pin is itself mounted in place and secured in such a manner that it can be blown loose.
In such an arrangement the casing, which typically is tubular, is secured to one part in the vehicle and another part of the vehicle is secured to a protruding end of the pin. Leads extend out of the rear end of the casing from the pyrotechnic charge to a controller so that the charge can be exploded to blow the pin out of the casing and thereby allow the two parts of the vehicle to separate, thereby initiating, for example, deployment of an air bag or locking-up of a seat-belt unwinder.
The main disadvantage of the existing systems is that the pyrotechnic charges, e.g. ignition charges or gas producers, as they are used for belt tighteners, air bags etc., have to be mounted in the release units before the release units themselves are installed in the vehicles. Since there is always the potential for accidental explosion of these charges, it is however desirable to install them as late as possible in the production process, thereby reducing to a minimum the possibility of accident. Furthermore, since the release units are normally made in special facilities and supplied assembled to the vehicle fabricators, the potential for accident is present during shipping and storage even before installation.